1820
| RANK | COUNTY | TOTAL POPULATION | RANK | COUNTY | TOTAL POPULATION | |
| 1 | Philadelphia County | 137,097 | 19 | Adams County | 19,370 | |
| 2 | Lancaster County | 68,336 | 9 | Allegheny County | 34,921 | |
| 3 | Berks County | 46,275 | 36 | Armstrong County | 10,324 | |
| 4 | Chester County | 44,451 | 27 | Beaver County | 15,340 | |
| 5 | Washington County | 40,038 | 16 | Bedford County | 20,248 | |
| 6 | York County | 38,759 | 3 | Berks County | 46,275 | |
| 7 | Bucks County | 37,842 | 33 | Bradford County | 11,554 | |
| 8 | Montgomery County | 35,793 | 7 | Bucks County | 37,842 | |
| 9 | Allegheny County | 34,921 | 37 | Butler County | 10,193 | |
| 10 | Franklin County | 31,892 | 45 | Cambria County | 3,287 | |
| 11 | Northampton County | 31,765 | 30 | Centre County | 13,796 | |
| 12 | Westmoreland County | 30,540 | 4 | Chester County | 44,451 | |
| 13 | Fayette County | 27,285 | 47 | Clearfield County | 2,342 | |
| 14 | Cumberland County | 23,606 | 22 | Columbia County | 17,621 | |
| 15 | Dauphin County | 21,653 | 39 | Crawford County | 9,397 | |
| 16 | Bedford County | 20,248 | 14 | Cumberland County | 23,606 | |
| 17 | Huntingdon County | 20,142 | 15 | Dauphin County | 21,653 | |
| 18 | Luzerne County | 20,027 | 28 | Delaware County | 14,810 | |
| 19 | Adams County | 19,370 | 41 | Erie County | 8,553 | |
| 20 | Lehigh County | 18,895 | 13 | Fayette County | 27,285 | |
| 21 | Union County | 18,619 | 10 | Franklin County | 31,892 | |
| 22 | Columbia County | 17,621 | 25 | Greene County | 15,554 | |
| 23 | Lebanon County | 16,988 | 17 | Huntingdon County | 20,142 | |
| 24 | Mifflin County | 16,618 | 40 | Indiana County | 8,882 | |
| 25 | Greene County | 15,554 | 50 | Jefferson County | 561 | |
| 26 | Northumberland County | 15,424 | 2 | Lancaster County | 68,336 | |
| 27 | Beaver County | 15,340 | 23 | Lebanon County | 16,988 | |
| 28 | Delaware County | 14,810 | 20 | Lehigh County | 18,895 | |
| 29 | Somerset County | 13,974 | 18 | Luzerne County | 20,027 | |
| 30 | Centre County | 13,796 | 31 | Lycoming County | 13,517 | |
| 31 | Lycoming County | 13,517 | 49 | McKean County | 728 | |
| 32 | Mercer County | 11,681 | 32 | Mercer County | 11,681 | |
| 33 | Bradford County | 11,554 | 24 | Mifflin County | 16,618 | |
| 34 | Perry County | 11,342 | 8 | Montgomery County | 35,793 | |
| 35 | Schuylkill County | 11,339 | 11 | Northampton County | 31,765 | |
| 36 | Armstrong County | 10,324 | 26 | Northumberland County | 15,424 | |
| 37 | Butler County | 10,193 | 34 | Perry County | 11,342 | |
| 38 | Susquehanna County | 9,960 | 1 | Philadelphia County | 137,097 | |
| 39 | Crawford County | 9,397 | 46 | Pike County | 2,894 | |
| 40 | Indiana County | 8,882 | 51 | Potter County | 186 | |
| 41 | Erie County | 8,553 | 35 | Schuylkill County | 11,339 | |
| 42 | Venango County | 4,915 | 29 | Somerset County | 13,974 | |
| 43 | Wayne County | 4,127 | 38 | Susquehanna County | 9,960 | |
| 44 | Tioga County | 4,021 | 44 | Tioga County | 4,021 | |
| 45 | Cambria County | 3,287 | 21 | Union County | 18,619 | |
| 46 | Pike County | 2,894 | 42 | Venango County | 4,915 | |
| 47 | Clearfield County | 2,342 | 48 | Warren County | 1,976 | |
| 48 | Warren County | 1,976 | 5 | Washington County | 40,038 | |
| 49 | McKean County | 728 | 43 | Wayne County | 4,127 | |
| 50 | Jefferson County |